1. Field of the Invention
The present invention relates to an image forming apparatus and a droplet discharge detecting method in the image forming apparatus.
2. Description of the Related Art
Generally, in inkjet recording devices, especially in a recording device provided with a head (linehead) as long as the width of paper, the head is not moved during printing and instead, a sheet of paper is conveyed directly beneath the head where ink is discharged onto the sheet so as to form an image thereon. In a printing method described above, when a nozzle is clogged and fails to discharge the ink, an image formation cannot be properly performed.
Thus, there is a need to dissolve clogging in a nozzle and hence, detection of a non-discharging state of a nozzle is performed first. Conventionally, there is a technology for detecting a nozzle in the non-discharging state (defect) by using a sensor formed by a pair of a laser diode (LD) and a photo diode (PD). Nozzles arranged in a row are caused to sequentially discharge ink droplets, and direct light or scattered light that appears when laser light emitted from the LD intersects the ink droplet is detected by the PD, thereby to detect a nozzle in the non-discharging state (defect).
Recent production of a high density and highly integrated head causes the time for detecting a nozzle defect to be increased significantly. In view of such a situation, Japanese Patent Application Laid-open No. 2006-110964, for example, discloses a technology that adopts a method for detecting a flying droplet either by tilting the direction of an optical axis of the detection light against the arrangement direction of the droplet discharging outlets and by performing control on the discharging timing of a droplet, or by performing control on a plurality of the nozzles in discharging droplets with shifted timing so that a plurality of droplets are kept in a state in which the droplets do not overlap each other within the cross section of the detection light. Accordingly, a plurality of droplets discharged from different droplet discharging outlets can be simultaneously detected, thereby achieving shortening of the detection time.
However, the conventional method for detecting a nozzle defect by having each nozzle discharge an ink droplet one by one has the problem in that it takes too much time in detecting the nozzle defect in a situation where a high density and highly integrated head is produced. The technology disclosed in Japanese Patent Application Laid-open No. 2006-110964 is capable of determining the number of ink droplets having been discharged simultaneously from a plurality of nozzles, but is incapable of determining which nozzle does have a defect.
Thus, there is a need to provide an image forming apparatus and a droplet discharge detecting method in the image forming apparatus capable of decreasing time needed for detecting a nozzle defect and further capable of identifying which nozzle does have the defect.